Wireless communications in general and, wireless cellular communications systems in particular, are becoming increasingly popular. Cellular communication systems are well known, and generally include cell sites, each of which serves a coverage area or cell. The cell site is the location within a cell that contains the hardware (e.g. an antenna, a radio base station, etc) required to communicate with a mobile end unit (e.g. a wireless mobile phone). The entire area over which service is provided is generally subdivided into a plurality of such cell sites, and channels are allocated to each cell site in accordance with a frequency reuse plan. A mobile end unit operating within a particular cell communicates with the cellular system through the cell site covering that cell. The various cell sites are typically connected either directly or, indirectly, to a land-line network, such as the public switched telephone network (PSTN).
Cellular communications systems originally were used to provide analog mobile telephone services. Today, cellular communications systems are used to provide a wide variety of wireless communication services. As used herein, the term wireless communication service is used to identify any logically discreet use of the wireless spectrum. Examples of such wireless services include analog mobile telephone service, digital mobile telephone service, personal base station (PBS) service, cellular office service (COS), and cellular digital packet data (CDPD) service. Personal base station service is provided using a PBS, which is a device that allows a cellular telephone to function as a cordless land-line telephone when used in the vicinity of the PBS. A PBS is usually located in the home and serves the cellular telephones within that home. COS is similar to PBS service, however COS is intended for use in an office environment as a wireless PBX. Accordingly, COS systems typically serve many more cellular telephones than does a PBS. A CDPD network is comparable to the cellular telephone network, except that data, rather than voice, is communicated between a mobile end unit and the PSTN or some other type of data network such as the Internet.
Wireless communication service providers are generally licensed to operate a wireless system in a particular geographic area using a specified frequency spectrum for radio communication between mobile end units and base stations. For example, a typical wireless service provider may have a license to operate in a 25 MHz spectrum. One-half of the spectrum (12.5 MHz) would be used for transmission by the base stations and the other half would be used for reception by the mobile end units. The 25 MHz spectrum may be divided into 416 channel pairs, each channel being 30 kHz wide. Each of the 416 channel pairs is capable of handling the communication between one mobile end unit and a base station. As indicated above, the wireless service providers are increasing the types of wireless services they provide and, the radio spectrum they license (e.g. 25 MHz, as in the instant example) must be shared among those different services.
For example, the wireless service provider, in addition to offering analog or digital cellular telephone service, may also provide PBS, COS and/or CDPD service. Analog or digital cellular telephone service is provided through the use of public cell sites. As discussed above, the entire area over which service is provided is subdivided into a plurality of such cell sites, and channels are allocated to each cell site in accordance with a frequency reuse plan, whereby customers in sufficiently separated cell sites use identical channels of communication without suffering any interference with each other. Because radio spectrum is a scarce resource, typically only 3 or 4 channels can be allocated to each cell site in such a system. The term "macrocellular system" is used hereinafter to refer to cellular systems with relatively large cell sites, such as an analog or digital cellular telephone system. The term "microcellular system" is used to refer to cellular systems with relatively small cell sites, such as PBS, COS, and sometimes CDPD systems, within the coverage area of the macrocellular system. The channels available to a microcellular system encompass a subset of the entire spectrum (i.e. not including, for example, testing channels, analog control channels, etc.) that the wireless service provider is licensed to use. A problem can arise when a system, which is not explicitly frequency planned, "pops-up" within the area serviced by a macrocellular system and begins using spectrum already allocated to the macrocellular system.
Consider a conventional radio base station of a macrocellular system that transmits and receives on its assigned forward and reverse channel pairs. In addition to monitoring the received signal strength (RSS) for information and/or interference on the reverse channel while transmitting on the forward channel, the base station also monitors the reverse channel (and/or the forward channel) at times when it is not transmitting on the forward channel and, accordingly, is not expecting to receive information on the reverse channel (and/or the forward channel). If the RSS on any one of its assigned channels not currently in use is above a predetermined threshold, indicating conflicting activity on the channel (one cause of which may be a cellular phone in a microcellular system establishing communication on the channel), the base station may react in a manner that negatively impacts its overall performance. For example, the base station may stop using the channel entirely, in which case, the base station may be left with an insufficient number of channels to handle call traffic during peak calling hours. The base station may alternatively ignore the disruptive use by the microceflular system and, may eventually assign one of its own calls to the channel. The microcellular system, like the radio base station of the macrocellular system, typically monitors the channel it is currently using for potential conflicting use and, will stop using the channel if conflicting use is detected thereon. Thus, although the base station's assignment of a call to the channel ideally will "scare away" the microcellular system, the microcellular system's delay in surrendering the channel will noticeably degrade the sound quality of the macrocellular system's call and vice versa.